Photographic silver halide materials are often chemically sensitized with one or more compounds containing labile atoms of gold, sulfur or selenium and the like to provide increased sensitivity to light and other sensitometric properties. Examples of typical chemically sensitized photographic silver halide emulsions are described in, for example, Research Disclosure, Item No. 308119, December 1989, Section III, and the references listed therein (Research Disclosure is published by Kenneth Mason Publications Ltd., Dudley Annex, 12a North Street, Emsworth, Hampshire PO 10 7DQ, England.) In Research Disclosure, Item No. 36544, September 1994, Section IV, page 510, there are a variety of chemical sensitizers disclosed.
Sulfur sensitizers are also disclosed in U.S. Pat. No. 5,415,992--Lok.
Thiourea compounds and sulfur sensitizers are disclosed in U.S. Pat. No. 4,810,626--Burgmaier et al and U.S. Pat. No. 5,213,944--Adin.